This invention relates to fluorescent lamps and more particularly to a fluorescent lamp which uses incandescent lamps as the lamp ballasting circuit.
Ballasting circuits are generally required for stable and efficient operation of fluorescent lamps. Under operating conditions, the lamp appears as a negative impedance device so a magnetic ballast device is normally used to provide a balancing positive series impedance thereby stabilizing operation. For certain applications, such as illumination sources in a photocopier machine, operating voltage requirements are such that the open circuit voltages must be higher than the ac line voltage (.apprxeq.105 VAC). In addition, a starting aid potential (SAV) required to initiate discharge is substantially higher (typically 450 volts peak) than the line voltage. Auxiliary starting circuits are generally used in these applications to provide the SAV for the relatively short time needed to initiate discharge. The conventional magnetic ballasts can be designed to provide the required open circuit and starting aid voltages while also providing current limiting and some level of regulation.
The conventional magnetic ballasts however, have some drawbacks, depending on use made of the lamp. For example, they do have appreciable weight which may be a detriment to portable applications. The magnetic ballast is also a relatively high cost item.
A potential answer to the above problems is the use of incandescent lamps to provide the required ballast characteristics. Such ballasting techniques are known in the art (see "Fluorescent Lighting Manual" by Charles L. Amick, published 1947 by McGraw Hill, pages 53, 53). Such techniques, while attractive because of the lower cost of incandescent lamps, however, have not proved commercially practical since it has proved difficult to provide an open circuit voltage that is higher than the line voltage.
It is, therefore, an object of the present invention to provide a fluorescent lamp incandescent ballasting system which provides reliable starting conditions.
It is a further object to provide a ballasting system which is lighter and less costly than magnetic ballast systems.